Alumina porcelain insulators for electrical apparatus



11, 1966 D. E. ALEXANDER ETAL 3,229,055

ALUMINA PORCELAIN INSULATORS FOR ELECTRICAL APPARATUS Filed April 19, 1961 2 Sheets-Sheet 1 INVENTO 1 W fl/PEM F077 1966 D. E. ALEXANDER ETAL 3,229,055

ALUMINA PORCELAIN INSULATORS FOR ELECTRICAL APPARATUS 2 Sheets-Sheet 2 Filed April 19, 1961 United States Patent 3,229,055 ALUMINA PORCELAIN INSULATURS FOR ELECTRICAL APPARATUS David E. Alexander, Rochester, N.Y., and Arem Fo'ti, Greensburg, Pa, assignors to I-T-E Circuit Breaker Company, Philadelphia, Pa., a corporation of Penn sylvania Filed Apr. 19, 1961, Ser. No. 104,050 11 Claims. (Cl. 200-48) Our invention relates to high voltage outdoor electrical apparatus supported by insulator stacks wherein each of the units in the insulator stacks is made of a high-strength wet-process fired alumina porcelain.

In the construction and use of outdoor disconnect switches and bus supports having ratings in the many thousands of volts, it is a common procedure to provide a spacing between the electrical current conducting parts and the supporting structures wherein the pacing is provided by means of wet-process porcelain insulators. The insulators serve a multiple function of not only providing the necessary basic impulse insulation level between the conducting parts and ground but also serve to provide all of the necessary electrical, mechanical and physical properties required. These insulating units are generally of the pin and cap variety or station post insulators and are made in a variety of configurations and shapes.

In the electrical industry there are fixed categories of Voltage ratings and thus insulators of particular dimensions and configurations have, in fact, been used in a clearly defined manner for the various categories. For example, on switches having 34.5, 46 and 69 kilovolts (kv.), the various cantilever, tensile, torsional and compression strengths required of the insulator and it associated hardware are such that all can be taken care of with standard insulators that have a 3" diameter bolt circle in their hardware and have a maximum outside diameter of 14" and a maximum height of 18". These wet-process fired porcelain insulators usually have a composition made of clay, feldspar and flint and, as a result, there is a considerable amount of quartz in the end product.

Higher voltage rated switches, as for example in the category of 115, 138 and 161 kv., have substantially long blades and, thus, substantially large accompanying weight so that there is a considerable amount of mechanical stress placed on the insulators and a sufliciently severe electrical stress required of the insulators that it is necessary that each of the insulator units be larger than the insulator units for the lower category of voltages aforementioned. Thus, for the group of switche having ratings of 115, 138 and 161 kv., it is usually necessary to have units which have at least a bolt circle in their hardware with a minimum diameter of the porcelain unit being 17".

It is an obiect of this invention to provide a novel type of insulator unit having the small dimensions of the insulator units normally used on the lower category of voltages and using these small dimension insulators on the higher rated category of switches, maintaining generally accepted electrical properties for the various voltage rat ings and developing adequate mechanical strength to suit the intended duty.

In the wet-process porcelain industry, as aforementioned, a frequently used composition of material used in making silica body porcelain is to provide a 40-60% clay, -30% hint or quartz, and 2040% feldspar. It has been known in the past that a substantially stronger insulator can be made by reducing the quartz or silica content of the insulator and this, in turn, can be achieved by replacing flint or quartz and feldspar with alumina (calcined alumina A1 0 and hydrates thereof). Although 3,229,055- Patented Jan. 11, 1966 such compositions have been known in the past, it has never been possible to fully utilize and take advantage of this desirable characteristic.

One reason that the alumina porcelain insulator has not received widespread use in the past is that although it can be fired in the same kiln at approximately 2300 F., the alumina is more expensive than the ingredients it replaces. Furthermore, the density of the fired alumina is extremely high, thereby resulting in heavier units, size for size. However, proper proportionment of physical size with respect to the more expensive, denser, and stronger material has made it possible to economically utilize in our invention the highly desirable characteristics of the alumina body porcelain units.

In a separate investigation We have found it is possible to make a light switch primarily due to the use of lightweight metal, such as aluminum, and providing both the necessary copper-to-silver contacts at all relatively movable parts, as well as the desirable transition from copperto-aluminum to prevent undesirable corrosive effects.

By making a susbtantial reduction in the weight of the switch for ratings of kv. and above, it is possible to use a 3" bolt circle insulator instead of the 5 bolt circle insulator. It the normal wet-process silica body porcelain insulator were to be used, there would not be suflficient mechanical strength for this switch in this size of bolt circle. However, by using an alumina body porcelain insulator, it is possible to substantially increase the mechanical strength characteristics of the insulator to take care of all of the requirement of the aluminum switch, 115 kv. and above, even though the dimensions of the stacking insulator units are no more than the dimensions normally used on switches 69 kv. and below.

Thus, with this arrangement, even though the alumina is more expensive than the flint or quartz and feldspar that it replaces, since the total size of the insulator is now substantially reduced, there is in fact an over-all saving in the cost of the insulator. Furthermore, even though the alumina has a substantially higher density than the flint or quartz and feldspar that it replaces, since the overall dimensions of the insulator are substantially smaller than the insulator that it replaces, the over-all weight of the unit is again substantially reduced.

In order to provide various combinations of units to achieve various basic impulse insulation levels (BIL) it has been found most economical to use only two basic heights of alumina porcelain insulator units. However, with our novel invention, we have found that we are able to make a single combination of alumina porcelain shells having substantially identical dimensions and configuration but to achieve two different heights of units by merely changing the height or length of the pin of the hardware.

In the prior art constructions, the silica insulator units have been constructed so that the hardware comprised of the cap and pin has a substantially higher mechanical strength than the silica poreclain, or to re-phrase this, there is a limit to the mechanical strength which can be obtained from the silica poreclain and this usually represents the weak link within a wet-process porcelain insulator since the hardware is stronger than the porcelain. When electrical switches are in a horizontal upright (insulators vertically disposed with the switch on top) or in the horizontal inverted (insulators vertically located with switch below insulator) there is a substantially equal force on all of the insulators and, hence, each unit within the supporting stack can be substantially identical in construction of porcelain and hardware. However, when the device is a vertically mounted switch (insulators disposed horizontally with the switch extending in a vertical direction) the insulator unit adjacent the base must withstand the cautilever force of not only the switch but all of the other insulator units in the stack. Thus, as a general rule, the prior art constructions utilizing silica porcelain and applied to 138 kv. switches in which the impulse levels have to be above 550 kv. BIL, it is necessary to provide a special insulator unit at the base with increased mechanical strength in order to withstand the additional cantilever force. This problem is described in detail in Electrical World, November 18, 1957 issue, in the article entitled Insulator Stack Rated for 138 kv. by H. B. Weaver appearing in the subsection entitled New Design Trend. However, with our novel construction, we are able to have a substantially high mechanical strength in the porcelain skirt portions of the insulator units so that all of the units in the insulator stack are identical, including the insulator unit located at the base, thereby eliminating the expensive and cumbersome arrangement heretofore required when it was necessary to provide for the increased basic insulation levels or the special mounting of the switch.

In the prior art constructions, the spacing between the outer circumference of the lower porcelain skirt and the closest point on the hardware was always substantially greater than the distance from the outer circumference on the lowest porcelain skirt and the plane at the bottom of the pin of the hardware. Thus, in order to obtain maximum benefit of the insulator, it was necessary to position a spacer below the insulator so that the latter aforementioned distance was not a weak point but instead was substantially equal in length to the former aforementioned distance. With our novel insulator, we have provided a construction wherein the latter of the two aforementioned distances is greater than the former of the two aforementioned distances so that the need for a spacer is completely eliminated, thereby saving material and economizing on the labor involved during manufacture and installation.

As previously noted, electrical apparatus of 115 kv. and above class require diameter bolt circles when silica porcelain insulator units were used, whereas with our unit a 3" diameter bolt circle is used with alumina porcelain units. This results furthermore in a substantial saving in the construction of the switch, since on a three insulator stack switch the two stacks located at the rear of the switch to support the operating mechanism can now be located closer to each other due to the smaller diameter of the porcelain skirts so that the mechanism on the switch can now be more compact. Furthermore, since the cap portion of the insulator unit is now only 3" instead of 5", it is possible to have a shorter blade of an electrical switch and still maintain the same open gap distance between the center insulating stack and the insulating stack supporting the jaw of the switch.

Accordingly, a primary object of our invention is to replace a regular flint feldspar or silica body wet-process porcelain insulator unit by a wet-process alumina body porcelain insulator which is smaller in size and weight but has greater mechanical and physical strength.

Another object of our invention is to utilize an alumina body porcelain insulator for aluminum switches in which the hardware of the insulators has 3" bolt circles even though the rating of the switch may be 115 kv. and above.

A still further object of our invention is to provide an insulator unit for high voltage outdoor switching apparatus and bus supports wherein the apparatus has a voltage rating of 115 kv. and above but the insulators have dimensions which do not exceed the dimensions which would normally be used on apparatus of 69 kv. and below.

Still another object of our invention is to provide an alumina porcelain insulator in which the outside diameter of the porcelain does not exceed 14" even though the insulator is used on switches and bus supports having ratings of 115 kv. and above.

A still further object of our invention is to provide an alumina porcelain wet-process insulator unit of two basic heights with the alumina porcelain shells being substan tially identical in dimensions and configuration with only the pin portion of the hardware differing in height.

Still another object of our invention is to provide an alumina porcelain insulator unit in which the alumina porcelain shells can be used with two different pieces of hardware to thereby result in different height units.

Still another object of our invention is to provide an alumina porcelain unit in which the cantilever strength of theporcelain is substantially increased so that the porcelain does not represent a weak link in the unit when elec trical switches are vertically mounted so that all of the cantilever force is adjacent the cap or when the switch is in a horizontal upright position when increased cantilever force is applied to the insulator unit adjacent the base.

Still another object of our invention is to provide a configuration for insulator units to be used on kv. electrical apparatus and above which does not requlrc the need for spacers in order to obtain the maximum benefit of the configuration of the insulator.

Another object of our invention is to provide a reduced size insulator unit having alumina porcelain shells that can be used on 115 kv. electrical apparatus so that there can be a substantial reduction in the length of the operating mechanism as well as the length of the blade without reducing the eifect of the operating mechanism or reducing the actual open gap length of the switch.

These and other objects of our invention will be more apparent when the preceding material is considered in conjunction with the following description and drawings, in which:

FIGURE 1 is a side view of an outdoor high voltage disconnect switch to which our invention is directed.

FIGURE 2 shows a portion of the insulator stacks of FIGURE 1 including the details of the dimensions wherein 18" insulators are made of an alumina porcelain with a 3" bolt circle for the hardware.

FIGURE 2A shows a view taken along the lines 2A 2A of FIGURE 2 showing the bolt circle of the hardware used.

FIGURE 3 illustrates a partial stack of insulator units similar to FIGURE 2 which shows the dimensions and constructions of insulator 14 /2" in height.

FIGURE 3A is a view taken in a direction of arrows 3A3A of FIGURE 3.

FIGURE 4 is a chart showing the electrical, mechanical and physical properties of the various constructions of insulators and makes a comparison between our novel alumina porcelain insulator and the silica porcelain insulator.

In FIGURE 1 there is shown a high voltage outdoor disconnect switch which functions and operates in substantially the same manner as disclosed in US. Patent 2,673,902 entitled Disconnect Switch issued March 30, 1954, to G. E. Heberlein, and assigned to the assignee of the instant invention.

The switch 10 comprises a base 11, insulator stacks 12, 13 and 14, and the conducting and operating portions of the switch 15. The disconnect switch 10 may be pro vided with surge protecting units 16 and 17 such as dis closed in applicants copending application Serial No.- 88,828 filed February 13, 1961, in the name of James B. Owens, entitled Disconnecting Swith With Surge Protection Gaps, now Patent No. 3,052,675 and assigned to the assignee of the instant invention. The main portion of the switch 15 contains terminal pads 18 and 19 in a jaw member 21. A complete current path is provided from the terminal pad 18 to the support 21, hinge 22, blade 23, flattened portion 24 to the jaw 20. The switch is operated from the arm 25 through the rotating insulator stack 12, operating mechanism 26 and 27. If desired, the switch can also be adapted with an arcing horn 28 having blade extension 29 cooperating therewith. If necessary, the switch It? can also be provided with a counter weight 30 in a manner well known in the art.

Recent developments in connection with high voltage outdoor disconnect switches has indicated that many of the prior obstacles can be overcome so as to result in substantial reductions in the weight of the switch as a result of the use of light-weight materials, as well as, in some instances, a reduction in the length of the blade. In the past it has not been possible to take advantage of the replacement of the normal copper conducting parts by light-weight conducting material such as aluminum. That is, numerous problems were encountered since it was not possible to have aluminum-to-aluminum contact between relatively movable conducting parts in view of the aluminum oxide coating that is formed thereon. It has been necessary to retain either a copper-to-copper or copper-tosilver relationship between relatively moving conducting parts. However, recent switches have provided a substantial improvement in the switch whereby most of the conducting parts are made of aluminum and providing a desirable transition from aluminum to copper to prevent corrosion therebetween. It is possible to have a majority of the switch made of aluminum and still retain the desirable characteristics of copper-to-copper or copper-to-silver at the relatively movable conducting parts. This feature is fully described and explained in copending application Serial No. 114,271 filed April 19, 1961 in the name of Arem Foti entitled Dual Metal Electric Switch, and assigned to the assignee of the instant invention.

Our invention is particularly adaptable to this type of switch wherein for a given voltage rating there is very substantial reduction in the weight of the conducting and operating parts over the prior art switch. Furthermore, other components of the switch, such as the base 11 can also be made of aluminum parts.

It is furthermore noted that in some installations there can be a substantial reduction in the length of the blade 23 for any given voltage range as a result of the judicious use of the surge protected gaps 16 and 17. This desirable feature is set forth in the aforementioned copending application Serial No. 88,828. Since either of these two arrangements, or the combination of these two arrangements, result in a reduction in the weight of the switch, we have found that the mechanical and physical requirements of the supporting insulator stacks 12, 13 and 14 is substantially reduced, thus giving rise to our instant invention.

In the past, the switch shown in FIGURE 1 having a rating of 69 kv. or below, could utilize wet-process porcelain insulators with a high silica content wherein the insulator had a 3" bolt circle on the hardware and a maximum diameter of 14". However, this insulator could not be used on disconnect switches of 115 kv. and above due to the extreme mechanical and physical properties placed on the insulators by the increased weight of the switch. Therefore, it was necessary in the past to use larger insulators and primarily those having bolt circles of 5 with a minimum diameter of 17 for the porcelain.

However, by using the features described in the aforementioned copending application Serial No. 114,271 and/or Serial No. 88,828 the mechanical and physical properties of 115 kv. outdoor disconnect switch is less than the prior art 115 kv. switches, although greater than the prior art 69 kv. switches. Thus, the standard prior art 3" bolt circle insulators of regular porcelain could not be used.

We have found that, notwithstanding the increased cost and weight density of alumina over silica, we are able to make an alumina porcelain insulator for 115 kv. switches and above which are more economical and weigh less than the regular porcelain insulator which would normally have to be used. To this end, we have taken several steps:

The first is that the composition of the wet-process porcelain insulator unit is such that the normal composition of -30% quartz or flint, 20-40% feldspar and 40-60% clay is altered to minimize the amount of flint or quartz and feldspar that is used. Thus, the composition of our alumina porcelain has 15-45% alumina,

6 20-40% feldspar, and 25-60% clay. This results in an end product which has a high modulus of rupture and more mechanical and physical strength than a regular porcelain insulator of equal dimensions.

These insulators are made in two basic heights, namely, 14 /2 and 18", as seen in FIGURES 3 and 2 respectively. The insulator units of FIGURE 2 have identical dimensions to those insulators which would normally be used singularly for a 46 kv. voltage rating and as set forth in NEMA Technical Reference Number 13 and the insulator units of FIGURE 3 have the same height as NEMA Technical Reference Number 14-0. However, by making these units of alumina porcelain rather than a silica porcelain, these units can now be used to provide basic insulation levels on apparatus having voltage ratings of 115, 138 and 161 kv. in the combinations and arrangements such as set forth in the chart of FIGURE 4. Thus, by the use of an alumina porcelain rather than the regular silica porcelain, it is possible to use a smaller size insulator for a given installation so that the end result is a more economical and lighter weight alumina porcelain insulator than the regular silica porcelain insulator which previously had to be used for that particular installation.

As seen in FIGURE 2, the insulator unit 40 is comprised of three shells or skirts 41, 42 and 43, containing hardware units 44 and 45 at the top and bottom respectively to act as securing means for interconnecting the individual insulator units to each other, as well as the end units of the insulator stack to the base and switch. A maximum diameter of the largest shell 41 is only 14" and the height of the insulator unit 40, including the hardware 44 and 45 is 18". The hardware unit 44, best seen in detail in the view .of FIGURE 2A, has a 3 diameter bolt circle for the bolts 46. The insulator units of FIGURE 3 likewise have three shells 51, 52 and 57 with hardware 54 and 55 attached to the top and bottom respectively. Another novelty of this invention, therefore, is the common use of the 14" diameter shell (41 of FIGURE 2 and 51 of FIGURE 3) and the 11" diameter shell (42 of FIGURE 2 and 52. of FIGURE 3), with the 7%." diameter shells (43 of FIGURE 2 and 57 of FIGURE 3) being similar on both the 14 /2 and 18 high units, With only the pin 45 being 3 /2 longer than the pin 55. The maximum diameter of the porcelain, which exists at shell 51, is 14" and the over-all height of the insulator unit 511 is 14 /2, including the hardware 54 and 55. The hardware has a 3" diameter bolt circle for the bolts 56 as best seen in FIGURE 3A.

A comparison of the various units is found in FIGURE 4 and below as follows:

The insulator unit 40 made of regular silica porcelain would weigh about 52 pounds, whereas the same unit of equal dimensions and as illustra-ted in FIGURE 2 made of alumina porcelain weighs 58 pounds. Iowever, for a given installation, as for example on a 650 kv. BIL 138 kv. voltage rating wherein three alumina porcelain insulator units 49 would be required, the weight would be 174 pounds, whereas the prior art constructions complying with NEMA Technical Reference No. 22 for substantially the same characteristics, would have a weight of 248 pounds, thereby resulting in a substantial weight saving by using alumina porcelain.

In like manner, the insulator unit 59 made of regular silica porcelain would weigh about 49 pounds, whereas the same unit of equal dimensions and as illustrated in FIGURE 3 made of alumina porcelain would weigh 55 pounds. However, for a given installation, as for example, on a 550 kv. voltage rating wherein 3 alumina porcelain insulator units 50 would be required, the weight would be 171 pounds, whereas silica body porcelain units complying with NEMA Technical Reference 19 would weigh 231 pounds.

For a 750 kv. BIL 171 kv. voltage rating wherein four alumina porcelain insulator units 50 would be required, the weight would be 220 pounds, whereas the prior art construction complying with NEMA Technical Reference No. 25 for substantially the same characteristics, would have a weight of 308 pounds.

In the illustration of FIGURE 1, the switch is mounted in what is commonly referred to as a horizontal upright in that the base 11 of the switch is at the bottom and a switch 10 is at the top. In this arrangement, most of the stress is placed on the pin 45 or 55 of the insulator. However, when the device is mounted in a horizontal inverted the insulator 4t and 50 stay in the position illustrated but the switch 10 and base 11 are interchanged with the base 11 at the top and the switch 10 located at the bottom. For this arrangement, the mechanical stresses are now placed on the cap 44 or 54 and the porcelain of the unit. Thus, when a silica body porcelain unit is used, it is necessary to de-rate the cantilever strength for cap mounted insulators. With silica body porcelain insulators and in accordance with present NEMA standards, the cantilever strength of the capmounted insulators are substantially less than that for pin mounted insulators. However, with the alumina porcelain body insulators for our invention, and as set forth in the chart of FIGURE 4, the cantilever strength is high .for either cap or pin mounting and the difference between these two is decreased. Thus, it is not neces sary to de-rate the cantilever strength for cap mounted alumina body insulators.

In some installations, as for example, on a 650 kv. BIL for 138 kv. electrical apparatus with the insulator applied horizontally, it is necessary to provide a special insulator at the base in order to provide the necessary mechanical strength. This is illustrated in the chart of FIGURE 4. However, with our alumina body porcelain units, the high strength of each of the units enables us to assemble the equipment with all of the units of the insulator stacks being identical in construction.

It will be noted that in the two insulator units shown in FIGURES 2 and 3 and identified by the numerals 755 and 754 respectively, there are two basic heights achieved rfor the unit, namely, 18" and 14 /2". It is noted that even though there are two basic insulator units, the porcelain portion of the units are substantially identical in configuration and dimensions and the only difierence exists between the pin 45 and 55 wherein the pin 45 is 3 /2" longer than the pin 55. Thus, by having a single basic porcelain body, it is possible to achieve all basic insulation levels merely by changing the pin and combinations of insulators when the porcelain is an alumina body.

In the prior art constructions which had a 5" diameter bolt circle, the outside circumference of the lowest shell was located very close to the plane containing the base of the insulator unit and, thus, in order to develop full di-electric properties of the stack, it was always mandatory to use 3 /2" high sub-base in connection with the insulator unit. However, the configuration and construction of our alumina body insulator permits us to eliminate the need for this sub-base and the stacking of our novel alumina body insulating units develops fully rated dielectric properties without the need of a sub-base.

In the foregoing, we have described our invention only in connection with preferred embodiments thereof. Many variations and modifications of the principles of our invention within the scope of the description herein are obvious. Accordingly, we prefer to be bound not by the specific disclosure herein but only by the appending claims.

We claim:

1. Electrical apparatus comprising a switch mounted on a base by a plurality of insulator stacks, each of said insulator stacks being comprised of wet-process porcelain insulator units having approximately 1545% alumina, each of said units having hardware securing means at the top and bottom for securing said unit to each other as well as to said base and said switch; said hard- 8 ware securing means having a three-inch diameter bolt circle, said electrical apparatus having at least a rating of kilovolts 2. Outdoor electrical apparatus comprising a switch mounted on a base by a plurality of insulator stacks, each of said insulator stacks being comprised of wetprocess porcelain insulator units having approxiately l5 45% alumina, each of said units having hardware securing means at the top and bottom for securing said unit to each other as well as to said base and said switch; said hardware securing means having a three-inch diameter bolt circle, said electrical apparatus having at least a rating of 115 kv.; the porcelain of said units having an outside diameter of 14".

3. A high voltage outdoor disconnect switch mounted on a base by a plurality of insulator stacks, each of said insulator stacks being comprised of wet-process porcelain insulator units having approximately 15-45% alumina, each of said units having hardware securing means at the top and bottom for securing said unit to each other as well as to said base and said switch; said hardware securing means having a 3 diameter bolt circle, said switch having at least a rating of 115 kilovolts; the porcelain of said units having a diameter of 14"; and each of said units being 14 /2 in height.

4. A high voltage outdoor disconnect switch mounted on a base by a plurality of insulator stacks, each of said insulator stacks being comprised of wet-process porcelain insulator units having approximately 15-45% alumina, each of said units having hardware securing means at the top and bottom for securing said units to each other as well as to said base and said switch; said hardware securing means having a 3" diameter bolt circle, said switch having at least a rating of 115 kv.; said units having a diameter of 14; each of said units being 18" in height.

5. A high voltage outdoor disconnect switch mounted on a plurality of insulator stacks; said high voltage switch being at least of the 115 kv. class; said insulator stack each being comprised of a plurality of insulator units in which each unit is comprised of wet-process fired alumina porcelain with hardware securing means on top and the bottom; said insulator units having a 14" outside diameter; said hardware securing means having a three inch diameter bolt circle.

6. A high voltage outdoor disconnect switch mounted on a plurality of insulator stacks; said high voltage switch being at least of the 115 kv. class; said insulator stack each being comprised of a plurality of insulator units in which each unit is comprised of wet-process fired alumina porcelain with hardware securing means on top and the bottom; said insulator units having a 14 out side diameter; said hardware securing means having a three inch diameter bolt circle; said insulator stacks capable of withstanding the mechanical and electrical strength required for switches having a normal rating of 115 kv. and above.

7. A high voltage outdoor disconnect switch mounted on a plurality of insulator stacks; said high voltage switch being at least of the 115 kv. class; said insulator stack each being comprised of a plurality of insulator units in which each unit is comprised of Wet-process fired alumina porcelain with hardware securing means on top and the bottom; said insulator units having a 14" outside diameter; said hardware securing means having a three inch diameter bolt circle; said insulator capable of withstanding the mechanical and electrical strength required for switches having a normal rating of 115 kv. and above; each of said insulator units having approximately 1545% alumina.

8. A high voltage outdoor disconnect switch being comprised of a base, a plurality of insulator stacks, mounted to said base, and carrying switch components; said switch components being made primarily of aluminum, said insulator stacks being comprised of wet-process por- 9 celain insulator units made of alumina porcelain with hardware securing means at each end; said hardware securing means having 3 bolt circles and the porcelain having a skirt diameter of 14", said disconnect switch having a voltage rating of at least 115,000 volts.

9. A high voltage outdoor disconnect switch being comprised of a base, a plurality of supporting insulator stacks mounted to said base and carrying switching means, said switching means movable from a first position to a second position for electrically connecting and disconnecting first and second terminals of said disconnect switch; said first and second terminals defining a switch open gap when said switching means is in its said second position; said switch having a voltage rating of at least 115 kv., said base having surge protected electrode electrically and mechanically mounted thereon and removed from said switch open gap; said insulator stacks being comprised of insulator units made of alumina porcelain with hardware securing means at each end; said hardware securing means enabling said insulator units to be bolted to each other to said base and to said switching means, said insulator having three inch diameter bolt circles and a diameter of 14".

10. A high voltage outdoor disconnect switch mounted on a base by a plurality of insulator stacks, each of said insulator stacks being comprised of wet-process alumina porcelain insulator unit having approximately 15-45% alumina, each of said units having hardware securing means at the top and bottom for securing said unit to each other as well as to said base and said switch; said hardware securing means having a three inch diameter bolt circle, said switch having three identical insulator units in each stack and having a basic impulse insulation level of 650 kv.

11. A high voltage outdoor disconnect siwtch mounted on a base by a plurality of insulator stacks, each of said insulator stacks being comprised of wet-process alumina porcelain insulator unit having approximately 1545% alumina, each of said units having hardware securing means at the top and bottom for securing said unit to each other as well as to said base and said switch; said hardware securing means having a three inch diameter bolt circle, said switch having at least a rating of 138 kv.; said units having a diameter of 14", said switch hav ing three identical insulator units in each stack and having a basic impulse insulation level of 650 kv.

References Cited by the Examiner UNITED STATES PATENTS 2,018,600 10/1935 Brown 174-209 X 2,063,953 12/1936 Pole 174209 X 2,697,144 12/ 1954 Owens 20048 2,771,522 11/1956 Hoye 20048 3,021,382 2/1962 Horrocks et al. u 174146 X 3,024,303 3/1962 Smothers et al. 174-209 X KATHLEEN I-I. CLAFFY, Primary Examiner.

RICHARD M. WOOD, Examiner. 

1. ELECTRICAL APPARATUS COMPRISING A SWITCH MOUNTED ON A BASE BY A PLURALITY OF INSULATOR STACKS, EACH OF SAID INSULATOR STACKS BEING COMPRISED OF WET-PROCESS PORCELAIN INSULATOR UNITS HAVING APPROXIMATELY 15-45% ALUMINA, EACH OF SAID UNITS HAVING HARDWARE SECURING MEANS AT THE TOP AND BOTTOM FOR SECURING SAID UNIT TO EACH OTHER AS WELL AS TO SAID BASE AND SAID SWITCH; SAID HARDWARE SECURING MEANS HAVING A THREE-INCH DIAMETER BOLT CIRCLE, SAID ELECTRICAL APPARATUS HAVING AT LEAST A RATING OF 115 KILOVOLTS. 